Autoantibodies against protein disulfide isomerase ER-60 are a diagnostic marker for low-grade testicular inflammation

Abstract

Study question: Is there a non-invasive biomarker for the diagnosis of testicular inflammatory lesions?

Summary answer: In sera from infertile azoospermic patients with histologically confirmed low-grade testicular inflammation, significantly elevated titers of autoantibodies against disulfide isomerase family A, member 3 (ER-60) were found.

What is known already: Infection and inflammation of the genital tract are supposed to be responsible for up to 15% of cases among infertile males. However, specific seminal or serological markers are not available to assess subacute or chronic inflammatory conditions in the testis.

Study design, size, duration: This study consisted of the identification of autoantibodies for testicular antigens in sera of patients with low-grade testicular inflammation, validation of candidates, development of an ELISA for the most promising target antigen and measurement of autoantibodies titers in healthy normozoospermic men (n = 20); male blood donors (n = 14); men with impaired semen quality without (n = 14) or with (n = 26) symptoms of genital tract infection/inflammation; azoospermic men with histologically confirmed testicular inflammatory lesions (n = 16); men after pharmacotherapy of genital tract infection/inflammation (n = 15) and men with acute epididymo-orchitis (n = 30).

Participants/materials, setting, methods: Proteins in lysates of normal testicular tissue were separated by high-resolution 2D gel electrophoresis and probed with sera of 13 patients with histologically confirmed chronic testicular inflammation. There were 14 proteins that immunoreacted with a majority of these sera and could be identified by mass spectrometry. Of these 14 proteins, disulfide isomerase family A, member 3 (ER-60), transferrin and chaperonin containing TCP1 complex, subunit 5 (epsilon) (CCT5) were considered as specific. Since ER-60 reacted with 92% of patient sera, an ER-60-autoantibody ELISA was developed.

Main results and the role of chance: The newly established ELISA detected significantly elevated titers of autoantibodies against ER-60 in the sera from infertile men with histologically confirmed chronic testicular inflammation (median 8.6; P < 0.01) compared with the control groups. Moreover, elevated levels of anti-ER-60 titers were detected in patients suffering from acute epididymo-orchitis (median 3.3; P < 0.05) as compared with healthy normozoospermic men (median 2.13; P < 0.001), male blood donors with unknown fertility status (median 2.72; P < 0.01), patients with impaired semen quality but no infection/inflammation (median 2.59; P < 0.001) and patients with symptoms of genital tract infections and/or inflammation (median 2.18; P < 0.001). Significantly lower levels of anti-ER-60 antibodies were measured in sera from patients after application of anti-inflammatory pharmacotherapy (median 1.9; P < 0.01) compared with those with histologically confirmed chronic testicular inflammation. The cut-off value of the assay was set to 6.6 U/ml based on a calculated sensitivity of 100% and a specificity of 81.2%.

Limitations, reasons for caution: The results obtained in this study showed statistically significant elevated titers of ER-60 antibodies in sera from patients with histologically confirmed testicular inflammatory lesions and from a few patients with acute epididymo-orchitis. However, the number of serum samples tested was limited. Severe testicular damage seen in azoospermic patients could represent a bias towards ER-60 reactivity, while the assay does not allow for different etiologies of the lesions to be distinguished. Due to ethical reasons, the prevalence of testicular inflammatory lesions among controls and non-azoospermic men cannot be studied at the histological level.

Wider implications of the findings: Measurement of ER-60 autoantibody titers in serum could be a novel non-invasive marker for the diagnosis of asymptomatic testicular inflammation causing male fertility disturbances.

Study funding/competing interests: This study was supported by a grant of the Deutsche Forschungsgemeinschaft (ME 1323/4-4) and the Translational Science Fund (Wirtschafts-und Strukturbank Hessen-WI Bank). M.F., A.P., W.W., H.-C.S. and A.M. are supported by the LOEWE focus group 'MIBIE' (Male infertility during infection and inflammation). The ER-60 ELISA is protected by a patent to the Justus-Liebig-University of Giessen with A.M. and M.F. as inventors (patent no. DE 10 2008 053 503). T.Z. as employee of the DRG Company was responsible for the ELISA development.

Keywords: ER-60; autoantibodies; immunological infertility; protein disulfide isomerase family A, member 3; testicular inflammation.